Iron-type golf club

ABSTRACT

As functions demanded for an iron-type golf club, (1) Spin performance, (2) Trajectory directivity, (3) Striking feeling, (4) Follow-through feeling, (5) Distance controllability, (6) Flyer improvement, and the like are mentioned. In order to satisfy these functions, it is devised to improve the properties of an iron-type golf club by subjecting particularly a soft iron forged head to surface treatment. 
     A foundation layer of an electroless Ni—P plating film is formed over the entire surface of a soft iron forged head and also a surface layer of an electroless Ni—P—W plating film is formed over the entire surface of the foundation layer. Heat treatment is performed at 300 to 700° C. when forming the electroless Ni—P—W plating film. The head is a wedge type head having a pitching wedge, an approach wedge, or a sand wedge.

TECHNICAL FIELD

The present invention relates to an iron-type golf club and more specifically relates to an iron-type golf club whose head is subjected to surface treatment.

BACKGROUND ART

Due to a revision of the rule of a golf club in golf game regulations, the “New Groove Regulations” enforced from 2010 prescribes the shape of grooves referred to as score lines of a face surface to a shape which does not easily apply a backspin. As the background, clubs with old grooves used so far have had spin performance which allows recovery even from a rough, which is deviated from a fairway, due to a miss shot in play. With respect to the situation, putting a golf ball in the rough is not regarded as a “miss”, and thus it is considered that a fair game property is lost, which leads to the establishment of the new rule. After the revision, the edges of the grooves are rounded to remarkably reduce the spin performance, which results in the fact that unpredictable behaviors are shown. More specifically, the control properties of a distance, a direction, and the like are impaired. In particular, a flyer has been likely to occur in a shot from a rough.

On and after Jan. 1, 2010, the new rule has been already applied to the main pro tours. On and after Jan. 1, 2014, the new rule is applied to elite amateur game lower tours. Moreover, on and after Jan. 1, 2024, it has been decided to apply the new rule also to general amateur levels and club game levels.

In order to improve the spin performance of an iron, an iron has been improved for the purpose of increasing the frictional resistance with a ball, e.g., an iron in which fine grooves are additionally processed in the face surface or the face surface is roughened (Patent Document 1) or an iron in which the repulsion is reduced by soft plating treatment (Patent Document 2) within the range of the regulations of the rule. As the surface treatment, two types, nickel plating and chromium plating, have been mainly used and have been used for the purpose of rust prevention and decoration. The film thickness has also been several microns to several tens microns.

Moreover, Patent Document 3 discloses an iron head for golf containing metal as the base material and having a layer in which a nickel film formed by electrolysis plating and a nickel-phosphorus (Ni—P) film and a nickel-phosphorus-tungsten (Ni—P—W) film, both of which are formed by electroless plating, are successively laminated toward the surface. Herein, the Ni—P—W plating film is provided due to high film strength and high wear resistance and in order to increase corrosion resistance against fertilizers, agricultural chemicals, and the like having strong corrosiveness. To that end, it is also disclosed to further form a chromate (Cr) film on the Ni—P—W plating film. However, the Ni—P—W plating film has never utilized so far in order to improve certain swing properties, such as striking feeling and follow-through feeling of an iron head.

For experienced golfers and professional golfers, a soft iron forged head is a special head in terms of good striking feeling. However, the soft iron forged head has many surface defects produced in a manufacturing process thereof, such as irregularities and pinholes. Therefore, in Patent Document 3, an electrolysis Ni plating layer is formed as a base, and then an electroless Ni plating layer is formed thereon to increase the corrosion resistance and decoration properties. In this connection with the situation, the soft iron forged head is devised to achieve striking feeling which is mild and desired by experienced golfers by heat treating the soft iron forged head to reduce the foundation hardness in a special case.

CITATION LIST Patent Literatures

Patent Document 1: JP-A No. 2010-110425

Patent Document 2: JP-A No. 2011-125542

Patent Document 3: Japanese Patent No. 2500159

Patent Document 4: JP-A No. H 11-76476

SUMMARY OF INVENTION Technical Problem

As functions demanded for an iron-type golf club, (1) Spin performance, (2) Trajectory directivity, (3) Striking feeling, (4) Follow-through feeling, (5) Distance controllability, (6) Flyer improvement, and the like are mentioned. The present inventors have found that various kinds of performance 1 to 6 which are problems to be solved can be noticeably improved by adjusting an impact surface of a face to a certain fixed surface roughness and employing an electroless Ni—P—W plating film in combination. More specifically, it is an object of the present invention to improve the properties of an iron-type golf club particularly by surface treating a soft iron forged head in order to satisfy these functions.

Solution to Problem

For solving the above-described problems, an iron-type golf club according to a first aspect of the present invention is configured so that a foundation layer of an electroless Ni—P plating film is formed over the entire surface of a soft iron forged head and also a surface layer of an electroless Ni—P—W plating film is formed over the entire surface of the foundation layer.

An iron-type golf club according to a second aspect of the present invention is configured so that a foundation layer of an electroless Ni—P plating film is formed over the entire surface of a soft iron forged head and a surface layer of an electroless Ni—P—W plating film is formed on a surface except an impact surface of a face and also an Ag plating film is formed on the impact surface of the foundation layer.

An iron-type golf club according to a third aspect of the present invention is configured so that a foundation layer of an electroless Ni—P plating film is formed over the entire surface of a soft iron forged head, a surface layer of an electroless Ni—P—W plating film is formed over the entire surface of the foundation layer, and further an Ag plating film is formed on an impact surface of a face of the surface layer.

In the invention according to the aspects described above, when forming the electroless Ni—P—W plating film, it is desirable to perform heat treatment at 300 to 700° C.

In particular, the effects of the present invention are noticeably demonstrated when the head is a wedge type head having a pitching wedge, an approach wedge, or a sand wedge.

Furthermore, it is preferable to increase the density of the Ag plating film by applying a mechanical impact thereto.

Advantageous Effects of Invention

In the iron-type golf club of the present invention formed as described above, due to the fact that the foundation layer of the electroless Ni—P plating film is formed over the entire surface of a soft iron forged head and also the surface layer of the electroless Ni—P—W plating film is formed over the entire surface of the foundation layer, (1) Spin performance, (2) Trajectory directivity, (3) Striking feeling, (4) Follow-through feeling, (5) Distance controllability, (6) Flyer, and the like are entirely remarkably improved as compared with former products having a chromium plating film and particularly an improvement of flyer is noticeable.

Moreover, also when the surface layer of the electroless Ni—P—W plating film is formed on a surface except the impact surface of the face and the Ag plating film is formed on the impact surface, the same improvement is observed and an improvement of striking feeling and flyer is noticeable. In particular, it has been found that good striking feeling, which has not been obtained so far, is obtained and the escaping property of a sole is excellent. Furthermore, due to the fact that a mechanical impact is applied to the Ag plating film formed on the impact surface of the face to increase the density, an improvement of striking feeling and an improvement of corrosion resistance can be achieved.

Due to the fact that heat treatment is performed at 300 to 700° C. when forming the electroless Ni—P—W plating film, it is presumed that the hardness of the Ni—P—W plating film becomes high but a low-temperature annealing action acts on the soft iron forged head to cause a physical property change of reducing the hardness of the soft iron foundation, which seems to lead to an improvement of striking feeling and the like.

The superiority of the iron-type golf club of the present invention has become noticeable by making a shot in a fairway, a rough, a divot mark, a bunker, and the like. In particular, even in the case of a lie in which a ball is buried, due to the fact that the Ni—P—W plating film is formed on the surface layer, resistance is hardly applied to a head sole portion, so that a result that the escaping property is very good is obtained. In usual, such a case results in bad results that power is not sufficiently applied to a ball due to resistance caused by grass or the golf club yields to the resistance in many cases but the iron-type golf club of the present invention can achieve a stable shot and can prevent a flyer even in such the state. Even when compared with usual products, the iron-type golf club of the present invention is excellent in the follow-through feeling in various situations. Moreover, when the spin amount is measured by a golf simulator, an increase in the spin amount can be confirmed in the golf club having the Ni—P—W plating film as compared with a commercially-available article having a chromium plating film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a head portion of an iron-type golf club.

FIG. 2 is a side view of the head portion of the iron-type golf club.

FIG. 3 shows Example 1 and illustrates a partial cross sectional view of a head in which a Ni—P—W plating film is formed over the entire surface.

FIG. 4 shows Example 2 and illustrates a partial cross sectional view of a head in which an Ag plating film is formed on an impact surface of a face and a Ni—P—W plating film is formed on a surface other than the impact surface.

FIG. 5 shows a modification of Example 2 and illustrates a partial cross sectional view of a head in which a Ni—P—W plating film is formed over the entire surface and an Ag plating film is formed on an impact surface portion of a face.

DESCRIPTION OF EMBODIMENTS

Next, the present invention is described in more detail with reference to embodiments shown in the accompanying drawings. FIG. 1 and FIG. 2 illustrate a head portion of an iron-type golf club according to the present invention and include a head 1, a shaft 2, a face 3, an impact surface 4, score lines 5, a hosel 6, a heel 7, a toe 8, a top 9, and a heel 10. In the general head 1, a central region including a sweet spot in the face 3 serves as the impact surface 4 and the score lines 5 formed by a plurality of concave grooves are horizontally formed in parallel in the impact surface 4. In the present invention, the shape of the head 1 is not particularly limited.

The present invention is targeted to an iron-type golf club in which the soft iron forged head 1 is subjected to surface treatment. In general, steel having a carbon content in the range of 0.02% to about 2% is classified into carbon steel and steel having carbon content in the range of 0.1% or less is classified into soft iron. In the golf industry, one referred to as a soft iron forged head also includes one which is not strictly soft iron but contains S25C (carbon content of 0.25%). Herein, various kinds of carbon steel are finely classified in such a manner that one having a carbon content of about 0.3% or less is classified into low carbon steel. Therefore, when referred to as “soft iron” in the present invention, steel equivalent to the “low carbon steel” is used in terms of the concept.

In general, the standard loft of a club is about 48° in the case of a pitching wedge (PW) and is about 56° in the case of a sand wedge (SW). In usual, since the loft of an iron is set at 4° intervals, it is difficult to achieve an intermediate distance (about 80 to 90 yards) when only the interval therebetween is 8°. Therefore, one having a middle degree between the angles of 52° is provided as an approach wedge (AW). Furthermore, in order to control a delicate carry, an approach wedge whose loft is adjusted at 2° intervals is also present. When the present invention is applied particularly to these wedge type soft iron forged heads 1, the effects are particularly noticeable.

FIG. 3 illustrates a first aspect of the present invention and illustrates a surface structure in which a foundation layer of an electroless Ni—P plating film 11 is formed over the entire surface of the soft iron forged head 1 and a surface layer of an electroless Ni—P—W plating film 12 is formed over the entire surface of the foundation layer. The foundation layer of the electroless Ni—P plating film 11 is provided in order to achieve the action as a buffer of absorbing a difference in the coefficient of thermal expansion between head materials and the electroless Ni—P—W plating film 12 and adhesiveness.

FIG. 4 illustrates a second aspect of the present invention and illustrates a surface structure in which the foundation layer of the electroless Ni—P plating film 11 is formed over the entire surface of the soft iron forged head 1 and the surface layer of the electroless Ni—P—W plating film 12 is formed on a surface except the impact surface 4 of the face 3 and an electrolysis Ag plating film 13 is formed on the impact surface 4 of the foundation layer.

FIG. 5 illustrates a third aspect of the present invention and illustrates a surface structure in which the foundation layer of the electroless Ni—P plating film 11 is formed over the entire surface of the soft iron forged head 1, the surface layer of the electroless Ni—P—W plating film 12 is formed over the entire surface of the foundation layer, and further the electrolysis Ag plating film 13 is formed on the impact surface 4 of the face 3 of the surface layer.

Herein, when performing partial plating, the partial plating is performed in such a manner that a surface except the plating target surface is masked, and then a plating film is formed only in the exposed portion. In usual, the Ni—P plating film and the Ni—P—W plating film are amorphous when the films are formed by electroless plating and are not subjected to another treatment. However, by heat treating the films then, the film state is changed to a crystalline state from the amorphous state, so that the hardness increases. Herein, the heat treatment temperature of the Ni—P—W plating film is usually 200 to 600° C. and preferably about 300° C. to 400° C. and the treatment time is 1 to 2 hours.

The Ag plating film 13 has defects that, when the Ag plating film 13 is formed by the electrolysis plating and is not subjected to another treatment, the density is insufficient, the hardness is excessively low, and corrosion and discoloration are likely to occur. Thus, in the present invention, by applying a mechanical impact to the Ag plating film 13 formed on the impact surface 4 of the face 3, and then performing, for example, shot blast treatment to increase the density, an improvement of striking feeling and an improvement of corrosion resistance are achieved.

The soft iron forged head is processed by repeating processes of heating→forging→annealing. In the soft iron forged head, the hardness of a head material sometimes vary even in the case of the same iron set due to a variation in temperature control also including a seasonal variation in a process of operation. Since a degenerated surface portion is formed into an oxidized scale to drop in the forging process, it is inevitable that the weight varies in manufacturing even in heads with the same number. Moreover, the soft iron forged head is heat treated (low-temperature annealing) to reduce the hardness of the head material, which is processed to be hardened, to thereby improve the striking feeling. Herein, in general, in carbon steel containing carbon in a proportion of 0.02% or more, the internal stress produced in the forging process is also removed by performing low-temperature annealing at a temperature (for example, 700° C.) equal to or lower than the A₁ transformation point.

In the present invention, the heat treatment temperature after the formation of the electroless Ni—P—W plating film is set to 300 to 700° C., whereby it is expected that the hardness of the Ni—P—W plating film can be increased and also the low-temperature annealing of the soft iron forged head can be performed in an accompanying manner, the hardness of the head material is reduced to improve the striking feeling, and the internal stress is removed.

In the electroless plating, the thickness of the plating film can be accurately controlled by controlling plating conditions, such as the plating bath composition, the temperature, and the plating time. More specifically, a plating film having an accurate thickness and an accurate weight can be formed on the surface of the soft iron forged head, the head weight variation can be adjusted by the weight of the plating film, and also the product quality can be increased. Moreover, since the electroless plating can form a plating film with a uniform thickness on the surface of a head of a complicated-shape, the weight balance of the head itself is not lost and the weight can be finely adjusted according to a user's preference.

EXAMPLES

A head of a sand wedge was subjected to various kinds of surface treatment. Then, five professional golfers actually hit a ball with the sand wedge in various field environments, and then the results were evaluated for six items. The six items include (1) Spin performance, (2) Trajectory directivity, (3) Striking feeling, (4) Follow-through feeling, (5) Distance controllability, (6) Flyer. The evaluation criteria are four stages of 0: Very good, o: Good, Δ: Average, x: Poor. Herein, the flyer refers to a state where grass is involved between a ball and the face surface in a shot from a rough, so that the ball slides to generate no backspin, which results in the fact that the ball does not stop within the expected carry of a used club. The striking feeling refers to a feeling in a shot. More delicate control can be achieved when the repulsion is lower. The follow-through feeling refers to lightness of a swing after a ball hits the impact surface of the face.

Example 1 corresponds to an article of the first aspect of the present invention. Example 2 corresponds to an article of the second aspect of the present invention. Comparative Example 1 is a commercially-available article having a chromium plating film. Comparative Example 1 is a development article having a Ni—P/PTFE (15%) composite film on the surface. Comparative Example 2 is a development article having a Ni—P/PTFE (30%) composite film on the surface.

Example 1

First, a foundation layer of a 22 μm thick electrolysis Ni—P plating film 11 is formed over the entire surface of a soft iron forged head 1. Then, a 10 μm thick electroless Ni—P—W plating film 12 is formed over the entire surface of the Ni—P plating film 11. The heat treatment conditions are a 330° C. air furnace and 1 hour.

An electroless Ni—P—W plating bath used herein is an aqueous solution containing tungstic acid and/or a salt thereof and containing phosphoric acid or a salt thereof in an electroless nickel plating bath. Table 1 shows a specific bath composition.

TABLE 1 Electroless Ni—P—W plating bath composition Chemical name Content Nickel sulfate 15 g/L Sodium tungstate 30 g/L Malic acid 1.5 g/L Sodium succinate 3 g/L Lactic acid 50 g/L Sodium hypophosphite 15 g/L Sodium hydroxide 5 g/L Ammonia water 1.5 g/L Lead nitrate 0.0003 g/L Surfactant 0.003 g/L

Table 2 shows the results obtained by evaluating the performance for the six items using the sand wedge subjected to the surface treatment of Example 1.

TABLE 2 Evaluation of Example 1 (Entire Ni—P—W film) Evaluation items A pro B pro C pro D pro E pro 1. Backspin performance ⊚ ◯ ⊚ ⊚ ◯ 2. Trajectory directivity ◯ ◯ ◯ ◯ ◯ 3. Striking feeling ⊚ ◯ ⊚ ◯ ⊚ 4. Follow-through feeling ◯ ◯ ◯ ◯ ◯ 5. Distance controllability ◯ ◯ ◯ ◯ ◯ 6. Flyer improvement ⊚ ⊚ ⊚ ⊚ ⊚ Evaluation criteria ⊚: Very good, ◯: Good, Δ: Average, X: Poor

The results show that the evaluation results are entirely high in all the items and that the flyer improvement is particularly noticeable and the striking feeling is also excellent.

Example 2

Next, a foundation layer of a 20 μm thick electrolysis Ni—P plating film 11 is formed over the entire surface of a soft iron forged head 1 in the same manner as in Example 1. The thickness of the foundation layer of an impact surface is 9 μm. Then, a surface layer of a 10 μm thick electroless Ni—P—W plating film 12 is formed on a surface except an impact surface 4 of a face 3 of the foundation layer. Heat treatment is performed in the state in a 330° C. air furnace for 1 hour. Finally, a 20 μm thick electrolysis Ag plating film 13 is formed on the impact surface 4. Then, the density of the Ag plating film 13 is increased by shot blast treatment. The shot blast treatment is not strong blast treatment of removing the material from the Ag plating film 13 but soft blast treatment.

An Ag plating bath is an aqueous solution containing silver cyanide and potassium cyanide. Table 3 shows a specific Ag plating bath composition.

TABLE 3 Ag plating bath composition Chemical name Content Silver cyanide  15 g/L Potassium cyanide 100 g/L

Table 4 shows the results obtained by evaluating the performance for the six items using the sand wedge subjected to the surface treatment of Example 2.

TABLE 4 Evaluation of Example 2 (Impact surface: Ag film, Another surface: Ni—P—W film) Evaluation items A pro B pro C pro D pro E pro 1. Backspin performance ◯ ⊚ ⊚ ◯ ⊚ 2. Trajectory directivity ◯ ◯ ◯ ◯ ◯ 3. Striking feeling ⊚ ⊚ ⊚ ⊚ ⊚ 4. Follow-through feeling ◯ ◯ ◯ Δ ◯ 5. Distance controllability ◯ ◯ ◯ ◯ ◯ 6, Flyer improvement ⊚ ⊚ ⊚ ⊚ ⊚ Evaluation criteria ⊚: Very good, ◯: Good, Δ: Average, X: Poor

The results show that the evaluation results are entirely high in all the items and that the flyer improvement is particularly remarkable. As compared with Example 1, a big improvement is observed in the “striking feeling” by changing the treatment of the impact surface of the face.

Comparative Example 1

Comparative Example 1 is a generally commercially-available chromium plating article. Table 4 shows the results obtained by evaluating the performance for six items using the commercially-available sand wedge.

TABLE 5 Evaluation of Comparative Example 5 (Chromium plating article) Evaluation items A pro B pro C pro D pro E pro 1. Backspin performance Δ X X X Δ 2. Trajectory directivity Δ Δ ◯ Δ X 3. Striking feeling Δ ◯ Δ Δ ◯ 4. Follow-through feeling Δ ◯ Δ ◯ ◯ 5. Distance controllability X Δ Δ Δ Δ 6. Flyer improvement X X X X X Evaluation criteria ⊚: Very good, ◯: Good, Δ: Average, X: Poor

The results show that the evaluation results are entirely low in all the items. The result is obtained that, after the revision of the rule, the flyer improvement is particularly inferior to those produced before the revision of the rule. A good result is not obtained also for the backspin performance.

Comparative Example 2

First, a foundation layer of a 22 μm thick electrolysis Ni—P plating film 11 is formed over the entire surface of a soft iron forged head 1 in the same manner as in Example 1. Then, a 10 μm thick Ni—P/PTFE composite plating film is formed over the entire surface of the foundation layer using a common electroless Ni—P/PTFE composite plating liquid. The PTFE content in this case is 15%. Table 6 shows the used electroless Ni—P/PTFE (15%) composite plating bath composition.

TABLE 6 Electroless Ni—P/PTFE composite plating bath composition (PTFE 15%) Chemical name Content Nickel sulfate 25 g/L Malic acid 10 g/L Lactic acid 23 g/L Sodium hypophosphite 25 g/L Ammonia water 5 g/L PTFE 2 g/L Surfactant 0.05 g/L

Table 7 shows the results obtained by evaluating the performance for the six items using the sand wedge subjected to the surface treatment of Comparative Example 1.

TABLE 7 Evaluation of Comparative Example 2 (Entire Ni—P/PTFE (15%) composite plating film) Evaluation items A pro B pro C pro D pro E pro 1. Backspin performance ◯ ◯ ◯ ⊚ ⊚ 2. Trajectory directivity ◯ Δ ◯ ◯ Δ 3. Striking feeling ◯ ◯ ◯ ◯ ◯ 4. Follow-through feeling Δ ◯ ◯ ◯ ◯ 5, Distance controllability ◯ Δ ◯ Δ Δ 6, Flyer improvement ◯ ◯ Δ Δ ⊚ Evaluation criteria ⊚: Very good, ◯: Good, Δ: Average, X: Poor

The results show that the evaluation results are slightly higher in all the items than the chromium plating commercially-available article but are entirely inferior to the articles of the present invention.

Comparative Example 3

First, a foundation layer of a 23 μm thick electrolysis Ni—P plating film 11 is formed over the entire surface of a soft iron forged head 1 in the same manner as in Example 1. Then, a 10 μm thick Ni—P/PTFE composite plating film is formed using a common electroless Ni—P/PTFE composite plating liquid over the entire surface of the foundation layer. The PTFE content in this case is 30%. Table 8 shows the used electroless Ni—P/PTFE (30%) composite plating bath composition.

TABLE 8 Electroless Ni—P/PTFE composite plating bath composition (PTFE 30%) Chemical name Content Nickel sulfate 25 g/L Malic acid 10 g/L Lactic acid 23 g/L Sodium hypophosphite 25 g/L Ammonia water 5 g/L PTFE 30 g/L Surfactant 0.05 g/L

Table 9 shows the results obtained by evaluating the performance for the six items using the sand wedge subjected to the surface treatment of Comparative Example 2.

TABLE 9 Evaluation of Comparative Example 3 (Entire Ni—P/PTFE (30%) composite plating film) Evaluation items A pro B pro C pro D pro E pro 1. Backspin performance ◯ Δ ⊚ Δ ◯ 2. Trajectory directivity Δ ◯ ◯ ◯ ◯ 3. Striking feeling ◯ ◯ ◯ ◯ ◯ 4. Follow-through feeling Δ Δ Δ ◯ ◯ 5. Distance controllability ◯ Δ ◯ ◯ Δ 6. Flyer improvement ◯ ◯ Δ ◯ ◯ Evaluation criteria ⊚: Very good, ◯: Good, Δ: Average, X: Poor

The results show that the evaluation results are slightly higher in all the items than the chromium plating commercially-available article but are entirely inferior to the articles of the present invention.

Table 10 collectively shows the mechanical properties of the heads of Examples and Comparative Examples.

TABLE 10 Properties of heads of Examples and Comparative Examples Comparative Comparative Comparative Example 1 Example 2 Example 1 Example 2 Example 3 Film type Impact surface NiP + NiPW NiP + Ag Cr NiP + NiP + Another surface NiP + NiPW NiP/PTFE15% NiP/PTFE30% Film thickness Foundation layer (μm) NiP: 22 Another Impact — NiP: 22 NiP: 23 (μm) surface: 20 surface: 9 Surface layer (μm) NiPW: 10 NiPW: 10 Ag: 20 — NiP/PTFE15%: NiP/PTFE30%: 10 10 Surface roughness Ra (μm) 0.99 1.303 1.128 1.684 0.939 (Impact surface) Ry (μm) 6.94 9.07 7.84 9.935 6.438 Rz (μm) 4.906 6.519 5.511 6.7 4.291 Coefficient of friction Coefficient of static 0.513 0.365 0.652 0.252 0.262 (Impact surface) friction Coefficient of dynamic 0.186 0.121 0.346 0.094 0.095 friction Hardness of impact surface (Hv) 966.5 95.1 935.7 738.4 487.4

It is considered that the sliding properties of a sole surface are improved by the Ni—P—W treatment (Example 1), which is shown in the follow-through feeling. The hardness is equal to that of a commercially-available “Ni+Cr plating finish” but the low coefficient of friction is linked to the numerical data. In the high PTFE content type (Comparative Example 2), an increase in the sliding properties can be expected in terms of the numerical value of the coefficient of friction. However, it is considered that the wear resistance in a shot leads to “releasing resistance” due to lack of the absolute hardness of the film. The low PTFE content type (Comparative Example 1) can also be expected because both high film hardness and sliding properties of the PTFE are achieved. As another specification, the specification of Face: Ag treatment+Another surface: Ni—P·W treatment (Example 2) is mentioned. It can be expected that, by performing Ag treatment of an ultra low hardness film of the face surface, “striking feeling” is additionally imparted in addition to the sliding properties of the sole surface subjected to the Ni—P—W treatment and a club which is very excellent in distance controllability is obtained.

REFERENCE SIGNS LIST

-   1 Head -   2 Shaft -   3 Face -   4 Impact surface -   5 Score lines -   6 Hosel -   7 Heel -   8 Toe -   9 Top -   10 Heel -   11 Ni—P plating film -   12 Ni—P—W plating film -   13 Ag plating film -   I Impact surface region 

1. An iron-type golf club comprising: a foundation layer of an electroless Ni—P plating film formed over an entire surface of a soft iron forged head; and a surface layer of an electroless Ni—P—W plating film formed over an entire surface of the foundation layer.
 2. The iron-type golf club according to claim 1, wherein heat treatment is performed at 300 to 700° C. when forming the electroless Ni—P—W plating film.
 3. The iron-type golf club according to claim 1, wherein the head is a wedge type head having a pitching wedge, an approach wedge, or a sand wedge.
 4. An iron-type golf club comprising: a foundation layer of an electroless Ni—P plating film formed over an entire surface of a soft iron forged head; and a surface layer of an electroless Ni—P—W plating film formed on a surface except an impact surface of a face and also an Ag plating film formed on the impact surface of the foundation layer.
 5. An iron-type golf club, comprising: a foundation layer of an electroless Ni—P plating film formed over an entire surface of a soft iron forged head; a surface layer of an electroless Ni—P—W plating film formed over an entire surface of the foundation layer; and an Ag plating film formed on an impact surface of a face of the surface layer.
 6. The iron-type golf club according to claim 4, wherein heat treatment is performed at 300 to 700° C. when forming the electroless Ni—P—W plating film.
 7. The iron-type golf club according to claim 4, wherein a mechanical impact is applied to the Ag plating film to increase density.
 8. The iron-type golf club according to claim 4, wherein the head is a wedge type head having a pitching wedge, an approach wedge, or a sand wedge.
 9. The iron-type golf club according to claim 5, wherein heat treatment is performed at 300 to 700° C. when forming the electroless Ni—P—W plating film.
 10. The iron-type golf club according to claim 5, wherein a mechanical impact is applied to the Ag plating film to increase density.
 11. The iron-type golf club according to claim 5, wherein the head is a wedge type head having a pitching wedge, an approach wedge, or a sand wedge. 